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What Is An Allergy?


An allergy is a body's reaction to something that normally does not provoke a response in a nonallergic person. Some people are born with a genetic makeup that causes their body to respond to certain "allergens" when exposed on repetitive occasions. 

Allergens can include:

  • Pollen
  • Dust mites
  • Mold spores
  • Animal dander
  • Insect stings
  • Medicines
  • Food

Some people have many allergies. Some have none. Allergy sensitivity may be linked to your genes and your environment. You have a higher risk of developing food allergies if your family members have them.

Allergic Reactions 

Allergic reactions may occur almost anywhere in the body but commonly affect the:

  • Respiratory system - Causing sneezing, runny nose, sinus congestion, coughing, wheezing or shortness of breath
  • Eyes - Causing tearing, itching or swollen eyelids
  • Skin - Causing itching or hives
  • Gastrointestinal tract - Causing abdominal pain, nausea or vomiting

If the whole body is involved in an abrupt reaction, shock and life-threatening anaphylaxis may occur. Fortunately, anaphylaxis is uncommon.

The part of the body affected by allergic reaction depends, in part, on the way you are exposed to an allergen. Respiratory symptoms occur when an allergen is inhaled. Gastrointestinal symptoms occur after ingestion. Itchy skin can occur after touching the allergen, such as poison ivy.

Food Allergy 

Common food allergens include:

  • Fish and shellfish (shrimp, lobster, crab)
  • Peanuts
  • Tree nuts
  • Eggs
  • Milk (mostly in children)

Symptoms may start quickly, within a few minutes. In less severe allergies, symptoms may start several hours after exposure. 

In case of severe symptoms, get to an emergency room immediately. Patients who have severe reactions may need to keep injectable adrenaline (e.g., an EpiPen) available. 

Treating Allergies 

The best treatment is to avoid allergens that will provoke a reaction.

When symptoms do occur:

  • Antihistamines can help control sneezing, itching, tearing and hives. 
  • Nasal sprays can reduce inflammation, swelling and mucus production.
  • Aerosol sprays into the lungs can help reduce asthma.
  • Decongestants can help reduce swelling and sinus pressure.
  • Immunotherapy (allergy shots) may reduce your sensitivity to allergens. 

Preventing Allergic Reaction 

Identifying the allergen, and then avoiding it, is the best way to prevent allergic reaction.

It may help to:

  • Use air purifiers, filters, humidifiers and conditioners to help rid allergens from the air inside.
  • Stay inside when pollen counts are highest.
  • Use allergen-proof mattresses and pillow covers.
  • Bathe pets regularly.


  • "Allergy," [] MedlinePlus.
  • "Food Allergy," [] MedlinePlus.
  • "Food Allergy," []National Institute of Allergy and Infectious Diseases.
  • "Hay Fever," [] MedlinePlus.
  • "Seasonal Allergies: Symptoms, Diagnosis, and Treatment," [] MedlinePlus.
  • "Pollen," [] National Institute of Environmental Health Sciences.
  • "Pets & Animals," [] National Institute of Environmental Health Sciences.
  • "Dust Mites," [] National Institute of Environmental Health Sciences.
  • "Mold," []National Institute of Environmental Health Sciences.


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Last Updated: 05-16-2016
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